U.S. patent application Ser. No. 10/286,015 entitled Apparatus and Method for Hardware-Based File System filed on Nov. 1, 2002 in the name of Geoffrey S. Barrall et al. and U.S. patent application Ser. No. 11/841,353 entitled Apparatus and Method for Hardware-Based File System filed on Aug. 20, 2007 in the name of Geoffrey S. Barrall et al, both of which are hereby incorporated herein by reference in their entireties, describe various filesystem structures that permit, among other things, a file server to maintain two copies of a filesystem, namely a current version of the filesystem and a prior “checkpoint” version of the filesystem. Specifically, the filesystem is maintained using tree structures that include a special root node that is actually a pair of structures referred to as the left hand side (LHS) and right hand side (RHS). In practice, one side is used to hold a “checkpoint” copy of the filesystem while the other side is used for ongoing management of the filesystem (including creation, deletion, and modification of filesystem objects). From time to time, the roles of the two sides reverse so that a “checkpoint” is taken using the side of the structure that was being used for ongoing management of the filesystem and ongoing management of the filesystem continues using the side of the structure that held the previous “checkpoint.” Two so-called dynamic superblocks are maintained for keeping track of the current and checkpoint versions of the filesystem.
One purpose of the “checkpoint” is to store a copy of the filesystem in case an error occurs during the ongoing management of the filesystem. Under certain circumstances, the filesystem may be reverted to the “checkpoint” version. One risk in such a system is that both the current version of the filesystem and the “checkpoint” version may become corrupted. Another risk is that an important piece of information will be removed or changed, and neither the current version of the filesystem nor the “checkpoint” version will include the original piece of information.